Cellular systems operate on the principle of frequency reuse which gives a cellular operator the ability to offer high radio traffic capacity. With higher radio traffic capacities, more users per geographic area are able to utilize radio communication. Frequency reuse, which is a core concept in cellular communication, involves reusing the same frequency in a system many times over to handle multiple calls. Time-division multiple access ("TDMA") is a form of access technology that allows multiple users to occupy the same frequency spectrum. Each user of the cellular system shares the frequency allocation with other users who have time slot allocation during other periods.
In a wireless local loop communication system using the TDMA standard of cellular communication, many users share the same frequency channel, each user being allocated a unique time slot. As traffic increases within each random access node, or cell site, the level of internal interference and signal blocking rises because the number of frequency carriers being used in neighboring, radio fixed parts increases. When a fixed access unit, or a mobile station, is engaged in a call, the user will experience quality problems as various factors affect the quality of radio communication, such as internal interference, blocking, load, multipath propagation, scattering and reflection. Prior attempts have been made to reduce such problems associated with the quality of calls.
Prior low-tier PCS communication systems have attempted to solve the problem of internal system interference and blocking by using dynamic channel allocation. In order to maintain the quality of radio communication within the cellular network, a fixed access unit, or mobile unit, will scan the operating environment and select all available channels. The scan result is then loaded in a history table in the order of its quality. The history table is updated at different time intervals to constantly monitor the condition of the various channels available for use. If a handset or mobile unit starts experiencing interference, fading, or receiving a stronger signal from another base station during the call, the mobile unit will automatically switch to a better channel based on the information loaded in the history table.
In a wireless local loop communication system, the distance between a random access node and a fixed access unit is much larger than the operating range of a business wireless system. A radio access node and a fixed access unit can be up to 3000 meters apart whereas in a business wireless system, the radio access node and fixed access units are usually up to 300 meters apart. The local channel condition can be quite different for a fixed access unit in these two systems because of the interference and blocking problems experienced by the radio fixed part. A channel sensed by the fixed access unit as a good channel might be a bad channel for a radio fixed part. A dynamic channel allocation system cannot tell the difference in channel quality and, hence, it will not effectively solve the problems associated with internal interference and blocking. As a result of this problem, the capacity of the cellular system is dramatically deteriorated as traffic rises. Therefore, a need exists for a method of system channel planning that will effectively solve the problems associated with internal interference and blocking in a wireless local loop communication system.